The present invention relates to a DC-DC converter and a wireless communication device including that DC-DC converter, and more particularly relates to a DC-DC converter suitable for reducing noise without increasing a circuit scale and a wireless communication device including that DC-DC converter.
A wireless communication device includes a voltage generation unit mounted therein which generates a voltage supplied to each functional block. In recent years, a DC-DC converter is provided as the voltage generation unit in place of an LDO regulator, in order to achieve low power consumption. However, there are problems that harmonic components (noise) generated because of a switching operation of the DC-DC converter degrade a reception sensitivity of the wireless communication device and degrade suppression of unwanted radiation of transmission.
U.S. Unexamined Patent Application Publication No. 2015/0002195 and U.S. Pat. No. 7,301,400 disclose solutions to these problems.
The configuration disclosed in U.S. Unexamined Patent Application Publication No. 2015/0002195 adjusts a frequency of a switching operation of a charge pump in accordance with an output voltage, thereby optimizing noise generated in the charge pump. However, in the configuration disclosed in U.S. Unexamined Patent Application Publication No. 2015/0002195, the frequency of the switching operation dynamically changes not only in a case where the output voltage changes but also in a case where an input voltage changes. Therefore, it is difficult to optimize the noise in a configuration in which the input voltage changes in a wide range.
On the other hand, the configuration disclosed in U.S. Pat. No. 7,301,400 converts an input voltage to intermediate voltages by using two DC-DC converters, respectively, and thereafter generates an output voltage by synthesizing the intermediate voltages. Phases of intermediate currents respectively output from the two DC-DC converters are shifted by 180 degrees with respect to each other. Due to this phase shift, the amplitude of an output current generated by synthesizing these intermediate currents becomes small, and therefore generation of the harmonic components (noise) can be suppressed.